There is a general tendency in the electronics industry towards producing semiconductor devices having smaller device dimensions to fabricate very large scale integrated and very high speed integrated circuits.
One of the problems encountered has been the difficulty of fabricating shallow junctions by doping. In fact, in the case of very shallow junctions, such as about 1500 angstroms and below, the depth the dopant elements reach due to implant channeling becomes an important issue. This is especially significant when dealing with relatively light dopants such as boron and phosphorus.
To avoid channeling, the semiconductor substrate, such as silicon, is typically preamorphized before implantation of the dopant. It would be desirable that such treatment of the substrate would render it amorphous to a well-defined depth beyond which essentially no crystal damage has penetrated. Then the dopant species could be implanted to that depth which keeps it completely in the amorphous region and, therefore, the dopant could not channel. Upon activation, the dopant could be made so as to diffuse just past the original amorphized interface and thereby provide a junction that is located in a fully defectfree region. However, this desired situation has not been fully realized or achieved. This is due to the fact that the preamorphization, itself, has been carried out by employing some type of implantation.
The customary implantations to date involve employing silicon or a heavy element such as germanium, tin, or indium in connection with boron type junctions, but such have not been entirely satisfactory. For instance, the use of silicon implantation into silicon has led to extended defects penetrating deeply beyond the amorphized region. Furthermore, when dealing with still shallower junctions, such as 1000 angstroms and below, it has been observed that the species, used to preamorphize, tend, themselves, to channel and lead to tails in the above 10.sup.16 /cm.sup.3 range which penetrate well-below the amorphized region and the intended junction depth.
Accordingly, it would be advantageous to preamorphize the semiconductor substrate without creating such an implant tail problem due to channeling.